1. Field of the Invention
The present invention relates to an image heating apparatus configured to heat a toner image on a sheet. This image heating apparatus can be used in an image forming apparatus such as a copier, a printer, a facsimile, and a multifunction peripheral having a plurality of functions of those apparatus.
2. Description of the Related Art
In a conventional fixing apparatus (image heating apparatus) of an electrophotographic image forming apparatus, a toner image formed on a recording sheet (paper) is heated and pressed at a nip portion between a fixing roller (first rotating member or endless belt) and a pressure roller (second rotating member or driving roller). In this way, a fixing process (image heating process) is performed.
In such a fixing apparatus, when the fixing process is continuously performed on recording sheets each having a width smaller than a maximum width applicable to the image heating apparatus, temperatures of regions of the fixing roller on end portion sides in a longitudinal direction thereof, which are out of contact with the recording sheet, may excessively rise in comparison with temperature of a central portion (hereinafter this phenomenon is referred to as “non-sheet passing portion temperature rise”).
As a countermeasure, in the fixing apparatus and the image forming apparatus described in Japanese Patent Application Laid-Open No. 2010-2691, when the non-sheet passing portion temperature rise occurs, a heat equalizing roller (heat conduction member or heat conduction roller) is brought into abutment against the pressure roller so as to disperse or transfer a heat of the pressure roller in the longitudinal direction thereof. In this way, a temperature distribution of the pressure roller in the longitudinal direction thereof is equalized. As a result, a temperature distribution in the longitudinal direction of the fixing roller in a contact relationship with the pressure roller is also equalized.
However, when the fixing process on the narrow recording sheets further continues, the temperature of the heat equalizing roller itself rises. As a result, even when the heat is equalized by bringing the heat equalizing roller into abutment against the pressure roller, the phenomenon of a non-sheet passing portion temperature rise of the fixing roller becomes unignorable.
As a countermeasure, it can be conceived that the pressure roller is cooled by blowing air from a fan onto the pressure roller. However, such a countermeasure may have an additional problem as follows.
Specifically, width sizes of the recording sheets which are subjected to image formation (pass through the fixing apparatus) vary from each other, and hence regions as non-sheet passing portions on the pressure roller vary correspondingly to such various width sizes. Thus, it is necessary to appropriately change the regions in which the pressure roller is cooled by an air.
In this way, in order to appropriately change the regions in which the pressure roller is cooled according to the various width sizes of the recording sheets, it is necessary to dispose a large number of fans in portions opposite to the pressure roller. In addition, it is necessary to determine the number of fans to be operated among the large number of fans according to a width size of a recording sheet. In this way, in addition to increases in size and cost, the control of the image heating apparatus inevitably becomes more complicated.